Light receiving element and method of manufacturing light receiving element

Abstract

A light receiving element includes a substrate including a silicon layer and a photodiode formed of a III-V group compound semiconductor and bonded to the silicon layer. The silicon layer includes a waveguide, the photodiode includes a first semiconductor layer, a light absorbing layer, and a second semiconductor layer, the first semiconductor layer is in contact with the silicon layer, the light absorbing layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to a surface of the first semiconductor layer in contact with the silicon layer, the first semiconductor layer has a first conductivity type, the second semiconductor layer has a second conductivity type, the first semiconductor layer includes a projecting portion and a first slab portion, and the projecting portion is connected to the first slab portion and projects from the first slab portion.

What is claimed is: 
     
         1 . A light receiving element comprising:
 a substrate including a silicon layer; and   a photodiode formed of a III-V group compound semiconductor and bonded to the silicon layer,   wherein the silicon layer includes a waveguide,   the photodiode includes a first semiconductor layer, a light absorbing layer, and a second semiconductor layer,   the first semiconductor layer is in contact with the silicon layer,   the light absorbing layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to a surface of the first semiconductor layer in contact with the silicon layer,   the first semiconductor layer has a first conductivity type,   the second semiconductor layer has a second conductivity type,   the first semiconductor layer includes a projecting portion and a first slab portion, and   the projecting portion is connected to the first slab portion and configured to project from the first slab portion so as to overlap the waveguide.   
     
     
         2 . The light receiving element according to  claim 1 ,
 wherein the projecting portion includes a first tapered portion, and   the first tapered portion has a shape tapering along a direction in which the waveguide extends.   
     
     
         3 . The light receiving element according to  claim 1 , wherein the projecting portion has a length of 2 μm or more. 
     
     
         4 . The light receiving element according to  claim 1 , wherein a distal end of the projecting portion has a curved shape. 
     
     
         5 . The light receiving element according to  claim 1 ,
 wherein the photodiode has a mesa,   the mesa includes the light absorbing layer and the second semiconductor layer, disposed on a top of the first slab portion, and faces the projecting portion in the direction in which the waveguide extends.   
     
     
         6 . The light receiving element according to  claim 5 ,
 wherein the mesa includes a second tapered portion,   the second tapered portion has a shape tapering along the direction in which the waveguide extends.   
     
     
         7 . The light receiving element according to  claim 6 , wherein the second tapered portion has a length of 5 μm or more. 
     
     
         8 . The light receiving element according to  claim 5 ,
 wherein the silicon layer includes a recessed portion and a second slab portion,   the recessed portion is a portion recessed from the second slab portion and disposed on each of two sides of the waveguide,   the waveguide is connected to an end portion of the second slab portion, and   the first slab portion of the photodiode is bonded to the second slab portion.   
     
     
         9 . The light receiving element according to  claim 8 ,
 wherein the second slab portion is configured to protrude more outward than the first slab portion,   the waveguide is configured to protrude more outward than the projecting portion.   
     
     
         10 . A method of manufacturing a light receiving element, the method comprising:
 bonding a photodiode formed of a III-V group compound semiconductor to a silicon layer of a substrate; and   forming a slab portion and a projecting portion in the photodiode,   wherein the silicon layer includes a waveguide,   the photodiode includes a first semiconductor layer, a light absorbing layer, and a second semiconductor layer,   the first semiconductor layer is in contact with the silicon layer,   the light absorbing layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to a surface of the first semiconductor layer in contact with the silicon layer,   the first semiconductor layer has a first conductivity type,   the second semiconductor layer has a second conductivity type,   the first semiconductor layer includes the projecting portion and the slab portion, and   the projecting portion is connected to the slab portion and configured to project from the slab portion so as to overlap the waveguide.